This study tests the drug, Plasmin (Human), in patients with a stroke due to a clot in the middle cerebral artery (MCA). Plasmin is an enzyme that causes clot lysis by cleaving a clot component, fibrin. In this study, Plasmin (Human) is administered locally through a catheter to the clot within 9 hours of the stroke onset. Three doses of Plasmin (Human) (20 mg, 40 mg, and 80 mg) are being tested in 3 different groups of patients. Patients are monitored by imaging of the affected artery and functional testing.